When an operating system is first loaded into a computer, it typically performs a few housekeeping tasks and then displays information on the computer's display device to tell the user of the computer system about the various stages of initialization being performed. However, before the operating system can display information on the display device it must know how to access the display device. Some computer systems, for example the IBM Personal Computer, have registers containing bits that define the particular type of display installed on the computer system. Because the operating system can read this register before any display of data is necessary, the operating system can determine the type of display. Once the operating system knows the display type, programming code already existing within the operating system can display information on the device.
This type of system has limitations, however, since only a limited number of display devices can be defined in a particular register. More importantly, before a new display type can be installed on such a system, the operating system must have been rewritten to provide programming code capable of using the new display type. Also, the shipment of the display type cannot occur until the new release of the operating system, capable of using the display type, is shipped and installed.
As more and more new types of display devices are introduced for new computer systems, this problem becomes more severe. If an operating system does not have a register, as described above, to define the type of display available, the operating system must use some other mechanism to determine which type of display is installed on the particular computer system or assume that one particular type is installed. This may also require that the operating system be capable of addressing all possible types of display devices that could be installed on the computer system, and if a new display type becomes available, it cannot be used on any computer system until the operating system has been modified to utilize it.
Another significant aspect of this problem occurs after the operating system has been modified to utilize the new display type. If the new version of the operating system expects to use the new display type as a console device, the new version cannot be installed until the new display is installed. Since the old version of the operating system cannot use the new display, both the new version of the operating system and the new display must be installed at the same time. This makes error detection very difficult, since it is very difficult to determine the location of a problem. That is, if nothing is displayed, is the display or the new version of the operating system at fault?
This problem is even more severe where the manufacturer of the display device is different from the manufacturer of the operating system. In this instance, considerable coordination between different companies must be established and maintained in order to utilize new hardware.
There is need in the art then for a common method of accessing any display device in order to display information on the display device. There is further need in the art for this method to be identical regardless of the type of display device. A still further need in the art is for such a method to be common for different types of processors. The present invention satisfies these and other needs in the art.